UPDATE 1-US safety panel says big Vytorin study can go on

* Merck gets green light after panel’s interim analysis

* Vytorin study expected to be completed by June 2013

* Cholesterol drug aims to prevent heart attacks, stroke

NEW YORK, March 11 (Reuters) - Merck & Co MRK.N on Thursday said an independent data safety monitoring board has approved continuation of a big study meant to determine whether its blockbuster Vytorin cholesterol drug prevents heart attacks and stroke.

Merck said a green light for the so-called “IMPROVE-IT” study to continue was given after the panel conducted an interim analysis of safety and efficacy trends in the study, which has enrolled nearly 17,000 patients worldwide. The trial, to eventually include 18,000 patients, is expected to be completed by June 2013.

“The interim efficacy analysis was conducted by the data and safety monitoring board after the trial had reached approximately fifty percent” of the 5,250 heart attacks, strokes and other cardiovascular events to be examined during the study, Merck said in a notice on its website.

Vytorin, which Merck now owns outright after acquiring its longtime partner Schering-Plough Corp last year, is considered one of the most potent medicines available for reducing levels of “bad” LDL cholesterol.

Vytorin and the related Merck cholesterol fighter Zetia have annual revenue of almost $5 billion, but sales of the medicines have plunged in the past two years due to several trials that cast doubt on their likely effectiveness.

The IMPROVE-IT study, because of its large size, is expected to give a definitive picture of Vytorin’s clinical effectiveness, and could rejuventate sales growth if the results prove favorable.

Some analysts have said clearcut favorable data could emerge long before the study is completed, and that the data safety monitoring board might therefore halt the study early.

Merck spokesman Lee Davies on Thursday said the board will conduct another interim analysis of the study after 75 percent of pre-specified cardiovascular events occur. (Reporting by Ransdell Pierson; Editing by Gary Hill)